Because of large AM-to-PM conversion or other phase deviation present in a non-linear amplifier, such as a limiting amplifier, a non-linear amplifier typically generates phase error caused from amplitude fluctuations. The amount of AM-to-PM conversion may be a critical factor when the non-linear amplifier is being used to detect phase information of the input signal by limiting the amplitude and to pass through to a phase detector.
The phase errors or phase deviations are related to harmonic distortions in a non-linear amplifier. Indeed, high-order harmonics are generated by the non-linear amplifier during strong non-linear operation like limiting action, and these high-order harmonics affect the phase deviation of the total waveform output by the non-linear amplifier. Typically, it is the phase deviation of the fundamental frequency that dominates the total phase deviation; however, the second and third harmonic can likewise cause significant degradation to phase deviation when the circuit is designed improperly or suboptimally. While phase distortion from harmonic distortions comes from the intrinsic nature of the non-ideal active device, the bandwidth limitation of the non-linear amplifier also generates zero crossing delay variations—that is, AM-to-PM conversion.
A bias-dependent, non-linear characteristic of a transistor, for example, used in a non-linear amplifier can generate phase deviation as well. One example is the bias dependence of the input capacitance of bipolar transistors. If the bias current is restricted, as in the case with mobile applications, slewing limitation may impose a significant contribution to phase deviation.
Accordingly, there is an opportunity in the industry for systems and methods for minimizing phase deviation and/or AM-to-PM conversion for dynamic range, radio frequency (RF) non-linear amplifiers.